Student DIY Microphone Workshop A simple, yet effective, student-built, phantom-powered, DIY microphone project for use in school audio/visual labs. Recommended for Grades 4-12
First, the Ground Rules: • Adult supervision is required. • Soldering irons are HOT! They melt metal and can easily burn skin. • Soldering should only be done by a qualified adult, and in a well-ventilated area away from the main assembly area. • Wear eye protection when cutting and stripping wires. • Assembly is not a race. Take your time to do it right.
Microphone theory of operation • Sound is waves of air pressure moving back and forth. • A microphone has a very small, lightweight surface that vibrates in response to sound waves. • Those vibrations are converted to waves of electricity inside the microphone. The waves of electricity are called the “signal.” • The signal can be amplified through a speaker or recorded electronically. Amp
Parts List • XLR connector • 47k Resistor • 0.1 μF Capacitor • Female micro-mini connector • Microphone capsule with connector
Other items • A soldering iron • Solder • Wire clippers • Wire strippers • Safety Goggles • An audio mixer or microphone preamplifier with an XLR input that supplies 48V Phantom Power. Headphones too!
Assembly Outline • Gather the parts on the list • Twist the capacitor and resistor together and cut the legs • Cut the red & black wires to 2-inches • Cut the black wire to 1-inch on the FEMALE connector • Strip the ends of the wires, and twist the ends • Bring your parts to the soldering table for soldering • Plug-in the capsule and Test the microphone • Assemble the microphone
Step 1 Twist the resistor and capacitor together.
Step 2 Cut the legs of the resistor and Capacitor to ¼ inch (6 mm)
Step 3 Cut the red & black wires to 2-inches (5 cm).
Step 4 Cut the black wire to 1-inch (2.5 cm) on the connector.
Step 5 Strip the ends of the wires, and prepare for soldering by twisting the ends of each wire. NOTE: Practice on the extra wire first!!! Twist eachwire end Practice on the extra wire first Finished connector
Step 6 Bring your parts to the soldering table for soldering. (Soldering must be done by an adult.) 3 2 1 Solder the resistor and capacitor where they are twisted together. Cut this soldered connection to ¼ inch (6 mm) Solder the black wire to this point. Solder the resistor to Pin 1 Solder the capacitor to Pin 3 Solder the red wire to Pin 2 c b a 47k 2 1 .1uF d 3 f e
Step 7 Connect the connectors together and test the microphone. Test the microphone by plugging it into a preamplifier or mixer which delivers 48V phantom power. Listen through headphones or a speaker output. “Click!” • If your microphone doesn’t work, try one of these: • Wrap the black wire/cap/resistor connection in tape • Try another capsule • Make sure it is correctly wired to Pins 1, 2, & 3 • Verify phantom power is on • Try a different XLR cable • Check the volume of the amplifier
Step 8 Assemble the microphone shell The black plastic parts are “keyed” so that they only fit one way into the metal shell.(Figures 1 & 2) Tighten the front and back together, so that the microphone element presses against the back of the rubber boot. (Figures 3 & 4) 1 Keys 3 4 2
Glossary • AC: Alternating Current. Electricity that flows back and forth like waves, alternating in direction. “Signal” is AC in our circuit. • DC: Direct Current. Electricity that only flows one way, direct from one point to another. “Power” is DC in our circuit. • k: kilo, or 1000. A 47k resistor is 47,000 Ohms of resistance. • Ohm: A unit of measure for resistors. More Ohms of resistance equals more restriction of electricity flow. • Phantom Power: 48 volts of DC power supplied on a 3-wire microphone cable. • μF: Microfarads. A unit of measure for capacitors. A 0.1uF capacitor stores 1/10,000,000 of a Farad of electrical charge. • XLR: A specific type of audio connector.
Appendix A: The Schematic A schematic (“skee-MAT-ick”) diagram is an engineering drawing of an electronic circuit: 3 2 1 < < < < . Schematic diagram 47k .1uF Assembly diagram How are they different? How are they the same?
Appendix B: Electronic Components • A resistor resists the flow of electricity. • A capacitor stores DC electricity. In our circuit, the 47k resistor is used to reduce the voltage to the microphone, from 48v to about 3v Resistor Schematic Symbol In our circuit, a capacitor is used to block the DC voltage used to power the microphone, but allow the AC signal to pass through. CeramicCapacitor Schematic Symbol
Appendix C: How It Works • The microphone capsule is powered by DC “phantom power” from the cable. • The microphone uses thepower to capture the signal, and returns the unused powerto the circuit through the 47k resistor. • The 47k resistor restricts the flow of unused power, then returns the remaining power to the circuit. • The 0.1uF capacitor blocks the unused DC power from getting to pin 3. . • The AC signal comes out of the microphone, passes throughthe capacitor, and into pin 3 of the cable, to the amplifier.
Appendix D: Questions • Does your microphone sound different than someone else’s microphone? • Why or why not? ___________________________________________________________________ • Why do you think it sounds different when you: • Talk into it from the side? The back? ____________________________________________________ • Hold it in your closed hand? ___________________________________________________________ • What happens if you choose a 1uF capacitor (Larger value) or a 10uF Capacitor (even larger value) rather than a 0.1uF capacitor? • Hint: Larger values reduce high-frequency output, like “hiss” in the letter “S”.__________________________________________________________________________________ • What do you think will happen if you choose a 4.7k (smaller) resistor, or a 1Meg Ohm (larger) resistor? _________________________________________________ • Hint: The resistor determines how much power gets to the microphone. • What happens if you plug in the capsule backwards (black-to-red?) • Hint: What happens when you look in a mirror? (Instructor Hint: Phase)__________________________________________________________________________________ • What happens if you put the resistor or capacitor in backwards? _______________ • Hint: Look for any markings on these components indicating which way they go. • What happens if you don’t plug the microphone into a source that supplies “phantom power?” ___________________________________________________________ • Hint: What happens if you don’t plug-in your TV?
Appendix E: Parts List * The red/black wire substitutes for a wired 2-pin Micro Mini connector set. The WM61A capsule should be prepared ahead of the workshop, by soldering red/black wires, or the male connector directly to the capsule. Pre-preparation saves time during the workshop.